Steering mechanism with planetary gear system and drive for impressing specific hand torque on the steering wheel

ABSTRACT

A motor vehicle steering mechanism is provided and includes a steering wheel fixedly connected to a steering column, a steering pinion meshing with a rack, a planetary gear system connected to the steering column and the steering pinion, wherein during a normal trouble-free driving operation the housing of the gear system is freely rotatable; an angle sensor detects the position of the steering column and/or steering wheel and generates a signal representative thereof, wherein a first drive applies torque directly to the steering column, and a second drive acts on the steering pinion or rack. The signal from the angle sensor is an input signal for an electronic control system that controls the second drive. A torque adjuster controls the first drive such that a hand torque corresponding to a driving situation is Produced for achieving a defined driving sensation for the driver on the steering wheel.

BACKGROUND OF THE INVENTION

The present invention relates to a motor vehicle steering.

A generic-type steering mechanism is known from DE 40 31 316 A1. Here, asuperimposing gear is proposed in the steering column, a gear which,depending on the steering angle velocity, superimposes an additionalsteering angle, by means of an electric motor, onto the steering gearconnected to the output side of the gear and therefore the steeredwheels. Therefore the gearing ratio of the steering mechanism can bevaried. In addition, steering intervention can occur independently ofthe driver's wishes when a stability control program kicks in.

These additional steering interventions cause an additional independentturning of the steering wheel due to the interconnection betweensteering wheel and steering gear. Therefore the input side of thesuperimposing gear must be assisted during the autonomous steeringintervention.

Torque suddenly arising in this way is disadvantageous. In particularthe system is virtually ineffective if the driver does not have a handon the steering wheel or the steering wheel for example is only heldwith very little force while driving straight ahead.

It is therefore an object of the present invention to improve ageneric-type steering mechanism in such a way that reactions ofautonomous steering intervention can be reduced or completelycompensated for and production of hand torque corresponding to thedriving situation can be achieved as simply as possible.

SUMMARY OF THE INVENTION

This object is achieved according to the invention by a steeringmechanism having a steering wheel that is fixedly connected to asteering column; a steering pinion that meshes with a rack; a planetarygear system having an input side connected to the steering column and anoutput side connected to the steering pinion, wherein the planetary gearsystem has a housing that during a normal trouble-free driving operationis freely rotatable; an angle sensor for detecting the position of thesteering column and/or the steering wheel and for generating a signalrepresentative of such position; a first drive for direct application oftorque to the steering column; a second or further drive for acting onthe steering pinion or the rack; an electronic control system forcontrolling the second drive, wherein a signal from the angle sensor isan input signal for the control system; and a torque adjuster or controlmeans for controlling the first drive such that a hand torquecorresponding to a driving situation is produced for achieving a defineddriving sensation for the driver on the steering wheel.

As regards the adjustment and control concept, the motor vehiclesteering mechanism according to the invention basically concerns asteer-by-wire steering mechanism, in which case however mechanicallinkage is provided between the steering wheel and the steered wheelsfor emergency use, that is to say in case of failure of the hand torquecontroller or the position adjuster for the steering rack and/or wheeladjustment. De-coupling between hand torque controller and positionadjuster is advantageously achieved as a result of the planetary gearhousing being mounted in such a way that it is freely rotatable. Theadjustment and/or control systems below and above the planetary gearsystem do not therefore interfere with one another or only slightly,since movements on the input or output shaft are compensated by turningof the planetary gear housing, without such turns becoming substantiallynoticeable on the other shaft.

Fail-safe mechanical linkage is ensured in a state of malfunction if thehousing is stopped in the event of trouble. This takes placeadvantageously by means of frictional or positive engagement. Thefrictional engagement can be realized for example by means of a disc ordrum brake. The frictional engagement however can also take place bymeans of two coupling discs, which in the state of malfunction arecompressed against one another by springs. In normal trouble-freedriving operation a coupling element is adjusted against the springforce with the aid of a coil based on the electromagnetic principle,whereby the coupling is disengaged and the housing of the planetary gearsystem is free to rotate. A coupling element can be advantageouslyintegrated for example into the housing, attached thereto or formed bythis itself. A positive engagement on the other hand can be realized forexample by means of toothed coupling elements. Also it is possible toprovide spring-tensioned pins, in the event of failure of a componentthe springs automatically forming a positive engagement with thehousing, wherein they lock for example in a recess or in borings of thehousing.

Advantageously, the hand torque is generated by means of a drive,whereby if a torque sensor is present torque adjustment can be provided.If no torque sensor is present, the hand torque may also be adjusted bymeans of a torque control system. In this case the drive acts on thesteering rack between the planetary gear system and the steering wheel.The drive for the torque-adjusted steering column is, from a controltechnology point of view, to be arranged as closely as possible on thesteering column and the steering wheel.

As a result of the freely rotating housing of the planetary gear system,which is advantageously designed as a planetary gear, the cinematicrelations of the planetary gear system for the torque adjuster and/orthe torque control system no longer have to be taken into considerationeither in normal driving operation or in the event of intervention by avehicle stability program (ESP), whereby the form of the controlalgorithm is not particularly complex and the torque adjuster can beoptimized with relatively little problem. In the simplest case, thetorque adjuster is a PID controller. However, it is equally possible todesign the torque adjuster as a state controller.

If a vehicle stability program superimposes an additional steeringangle, the rack of the position adjuster is adjusted accordingly by theservo-drive. A reaction on the steering wheel is compensated to a largeextent by the freely rotating housing of the planetary gear system andtotally with the aid of the hand torque control and/or adjustment systemso that advantageously the person steering the vehicle does not feel theautonomous steering intervention by the vehicle stability program. In aparticular embodiment it is also, however, possible without any problemto inform the person, in particular during the autonomous steeringintervention by the vehicle stability program, of its activity via thesteering wheel. For this purpose, an additional hand torque or torqueprogression can be superimposed over the normal hand torque, similar tothe vibrating and/or shaking of the brake pedal in the event of responseby the ABS, as a consequence of which vibration on the steering wheelcan be felt for example.

The drive for generating the hand torque is advantageously activelyconnected by means of a non-self-locking gear to the steering column ordirectly to the steering wheel, so that even in the event of failure ofthe drive and mechanical linkage from the steering wheel to the steeringpinion the steering wheel can be steered by the driver.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of a motor vehicle steering mechanism according to theinvention is described in detail below on the basis of figures, wherein:

FIG. 1 shows in a schematic diagram a motor vehicle steering mechanismaccording to the invention;

FIG. 2 a motor vehicle steering mechanism according to FIG. 1 withassociated control concept;

FIG. 3 a a hollow shaft motor for direct drive of and 3 b the steeringcolumn.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In FIG. 1 a motor vehicle steering mechanism according to the inventionis schematically illustrated. The steering mechanism has a steeringwheel 1, which rigidly acts for example by means of a universal joint 1a on an input shaft 2 of a planetary gear system 4. The planetary gearsystem 4 also has an output shaft 11, which is connected to a steeringpinion 5. The steering pinion 5 as presently known in turn meshes with asteering rack 6, which causes a wheel angle change of the steered wheelsin the vicinity of the steered axle of a motor vehicle by means of trackrods 7 when the steering pinion 5 is turned.

The planetary gear system 4, which can be designed as a planetary gear,supports a drive 3 on an outer side in the form of an electric motor,which moves the steering column 2 by means of a belt drive 15, 18. Anelectric servo-drive 8 is assigned to the steering rack 6 and by meansof a pinion 9 and a toothed belt acts on a circulating ball 10, whichengages with a thread adapted thereto, so that a turn of the circulatingball 10 likewise causes a displacement Δx of the steering rack 6 andthus a wheel angle change.

An angle sensor 12 arranged on the steering column 2 determines theposition of the steering wheel 1 and generates a corresponding signal,which as shown in FIG. 2 is fed to the position adjuster 22 foradjustment of the steering rack 6, as well as the torque adjuster 21, 23for adjustment of the hand torque. A torque sensor M is also arranged inthe steering column 2, which determines the hand torque impressed on thesteering wheel 1. The signals of the torque sensor M likewise representan input quantity of the torque adjuster 21. If instead of a torqueadjustment system a torque control system is used, the torque sensor Mcan be dispensed with.

So that mechanical linkage from the steering wheel 1 to the steeringpinion 5 is possible in the event of a fault, the housing of theplanetary gear system 4 is stopped if a fault occurs. A coupling, thecoupling elements 16, 17 of which are compressed together in the eventof malfunction by means of a spring force 20, serves this purpose.Either positive or frictional engagement can be produced by compressingthe coupling elements 16, 17 together. In normal trouble-free drivingoperation, a current-conducting coil produces a magnetic field, as aresult of which coupling element 16 is held against the spring force 20away from the coupling element 17, so that the housing of the planetarygear system 4 can rotate freely. In the event of a fault the coil 20does not conduct current, whereby the spring 20 compresses couplingelements 16, 17 against one another. Positive engagement can be easilyobtained for example by teeth of the coupling elements.

A damping element 14 can be arranged between steering pinion 5 andoutput shaft 11 of the planetary gear system 4 for better de-coupling ofposition adjuster 22 and torque adjusters 21, 23.

Depending on the control concept and presence of a torque sensor thehand torque is either controlled (no torque sensor available) oradjusted (torque sensor available). For torque adjustment, measurementof at least a torque in the section between the pinion and the steeringwheel is necessary.

As illustrated in FIG. 2, the turn of the steering wheel 1 is sensed bymeans of the angle sensor 12, which produces the desired quantityφ_(steer, desired). This desired quantity is at the same time the inputquantity for the characteristic field 23. Possible additional auxiliaryvariables, for example vehicle speed, may serve as additional inputquantities for the characteristic field 23, by means of which thereference signal T_(sensor, ref) (desired torque) is produced and theinput quantity for the torque control system 21, which produces thecontrol quantity i_(motor, SI) for the drive 3. Because the housing ofthe planetary gear system can rotate freely, turning of the pinion 5does not or only slightly influences the hand torque. On the other handturning of the steering column 2 by the drive 3 does not cause adisruptive torque on the steering pinion 5. Therefore the positionadjuster 22 is de-coupled by the torque control, which serves to adjustthe steering rack 6. The steering rack 6 is connected via the track rods7 to the steered wheels (not shown), as a result of which adjustment ofthe rack 6 leads to adjustment of the steered wheels. The auxiliaryangle φ_(ESP) is locked on the desired quantity φ_(steer, desired). Thesum of these two angle quantities is an input quantity φ_(pinion, ref)of the position adjuster 22. A further input quantity of the positionadjuster 22 is either the position of the pinion 5 or the position ofthe steering rack 6. In FIG. 2 the angle position of the pinion 5 ismeasured by means of the angle sensor 13, whereby the angle sensor 13transmits the actual signal φ_(pinion, actual) to the position adjuster22. The position adjuster 22 produces the desired currenti_(motor, rack), which serves to control the rack motor 8.

The torque control illustrated in FIG. 2 as input quantity has the handtorque on the steering wheel 1, which arises by means of the torquesensor M, generating the signal T_(sensor, actual). The torque sensor Mcan be arranged at any arbitrary place in the steering mechanism abovethe planetary gear system 4. However, it is expedient to arrange thesensor M as tightly as possible on the steering wheel 1, so that thetorque adjuster 21 can be realized as simply as possible.

FIGS. 3 a and 3 b show two different views of an alternative drive forgenerating the hand torque by means of two electric motors 24 a, 24 b,the common rotor 26 of which is rigidly connected to the steering column2. They form a redundant system, whereby the motors 24 a, 24 b are sodimensioned that one motor can generate the hand torque in each case.

The specification incorporates by reference the disclosure of PCT/EP02/13603 filed Dec. 2, 2002 and German priority document 101 607 17.2 filedDec. 11, 2001.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. A motor vehicle steering mechanism, comprising: a steering wheelfixedly connected to a steering column; a steering pinion that mesheswith a rack; a planetary gear system having an input side connected tosaid steering column and an output side connected to said steeringpinion, wherein said planetary gear system has a housing that during anormal trouble-free driving operation is freely rotatable; an anglesensor for detecting the position of at least one of said steeringcolumn and said steering wheel and for generating a signalrepresentative of such position; a first drive for direct application oftorque to said steering column; a second drive for acting on saidsteering pinion or said rack; an electronic control system forcontrolling said second drive, wherein the signal from said angle sensoris an input signal for said control system; and a control means forcontrolling said first drive such that a hand torque corresponding to adriving situation is produced for achieving a defined driving sensationfor a driver on said steering wheel.
 2. A steering mechanism accordingto claim 1, wherein a brake means is provided for effecting at least oneof decelerating and stopping said housing of said planetary gear system.3. A steering mechanism according to claim 1, which includes means forpositively or frictionally blocking a movement of said housing of saidplanetary gear system upon disruption of said first drive or ofcomponents associated therewith.
 4. A steering mechanism according toclaim 1, which includes means for blocking a relative movement betweensaid housing of said planetary gear system and said steering column, orbetween said housing and said steering pinion, upon disruption of saidfirst drive or of components associated therewith.
 5. A steeringmechanism according to claim 1, wherein a torque sensor M is providedfor detecting a hand torque impressed upon said steering wheel and forgenerating a representative signal.
 6. A steering mechanism according toclaim 5, wherein said control means is in the form of a torque adjusterthat controls said first drive on the basis of at least one of saidsignal from said angle sensor and the signal from said torque sensor M.7. A steering mechanism according to claim 6, wherein further vehiclecondition parameters form input quantities for said torque adjuster. 8.A steering mechanism according to claim 1, wherein said first drive is ahollow shaft motor having a rotor that is fixedly connected with saidsteering column.
 9. A steering mechanism according to claim 1, whereinsaid first drive drives said steering column by means of least one of anintermediate gear mechanism and belts.
 10. A steering mechanismaccording to claim 9, wherein said belts are toothed belts.
 11. Asteering mechanism according to claim 1, wherein a further redundantdrive is provided for producing hand torque in the event of failure ormalfunction of said first drive.